1. Field of the Invention
The present invention relates to vehicles in which two or more driven wheels are each connected to an individual electric motor yet driven by a single controller. More particularly, the present invention relates to methods and apparatus for adjusting one or more motors in response to the detection of one or more conditions that indicate that the operator of the vehicle is attempting to drive the vehicle straight on approximately level ground.
2. Description of the Related Art
Electric vehicles such as power chairs and electrically driven wheel chairs have traditionally been manufactured with two wheels, each typically driven by a separate motor. Therefore, two different motors function to separately control a left and a right wheel. A user control such as a throttle or joystick is traditionally used to operate such a vehicle. User movements that are input via the user control are then converted into voltages by a motor controller. These voltages are then used to drive the left and right motors so that the left and right wheels rotate and cause the vehicle to advance in a desired direction. For example, when a user wishes to turn the vehicle left, the motor controller will interpret the movement in the user control and convert the position of the user control into voltages that control the wheels such that the voltage provided to the left wheel is less than the voltage provided to the right wheel.
When a user pushes a user control such as a joystick, he or she expects the desired movement to control the vehicle in an expected manner. For example, when the user pushes the joystick straight ahead, it is expected that the vehicle will drive straight. However, electrical and mechanical differences between the motors that drive the left and right wheels can cause the motors to run at different speeds than expected. As a result, these slight variations present in the two motors, gear boxes or other drive train related components can cause the vehicle to drive in an unexpected, unpredictable, and undesirable manner.
In order to compensate for such disparities between drive train related components, gear boxes, and/or driving motors, the motors are typically tested when they are received from the assembly line at the manufacturer of the vehicle. At this time, the manufacturer uses this testing to identify well-matched pairs of drive train related components (e.g., motors). However, this testing process is a costly and time-consuming one. Moreover, even closely matched motors will display differences in operating characteristics (e.g., reduction in motor speed) due to electrical and mechanical differences. A handheld programmer is therefore typically used to adjust a xe2x80x9ctrimxe2x80x9d parameter that accounts for such differences. In other words, this xe2x80x9ctrimxe2x80x9d parameter compensates for differences between the motors present upon initial production. However, it is important to note that this xe2x80x9ctrimxe2x80x9d parameter is a permanent, fixed parameter.
Although the xe2x80x9ctrimxe2x80x9d parameter compensates initially at xe2x80x9cproduction timexe2x80x9d for differences between motors, motor operating characteristics can change over time. For example, a commonly used motor technology is brush direct current (DC) motors. These brushes are applied with pressure to provide voltage to the motor. However, these brushes wear over time and therefore the characteristics of the brushes change, which can reduce the voltage that is provided to the motor. Unfortunately, the fixed xe2x80x9ctrimxe2x80x9d parameter that is traditionally used to compensate for variations in the electrical components cannot compensate for changes in those components that occur over time.
Another difference between motor operating characteristics that cannot be compensated for during original production of the vehicle occurs when one of the motors is replaced. It is not uncommon for a motor to fail mechanically. When a motor needs to be replaced, the vehicle is brought to a dealer to replace the nonfunctioning motor. However, unlike the original manufacturer, the dealer does not have the resources or the capability to reset or modify the trim parameter that was fixed by the manufacturer of the vehicle.
Similarly, motor operating characteristics can change over time as a result of motor or vehicle use. For example, when one of the tires loses air, this creates a drag on the tire and associated wheel. As another example, the operating characteristics of gear boxes can also change over time. Since the trim parameter is a fixed, static parameter that is established during production of the vehicle, the trim parameter no longer compensates for mechanical and electrical differences between the motors. Unfortunately, many repair centers do not have the capability to reset the trim parameter.
Even characteristics of the individual operating the vehicle can effect the way that motors operate. For example, a heavy person who slouches may put greater pressure on one of the wheels. However, a trim variable that is fixed at production cannot compensate for operating characteristics that vary over time that result from motor use, vehicle use, or characteristics that are unique to the individual operating the vehicle.
Since a trim variable is a static variable fixed at production time, an individual must typically compensate for undesirable operating conditions that occur after the vehicle is purchased. For instance, when operation of one of the motors deteriorates gradually over time, the operator of the vehicle must actively and continually compensate for the offending motor by modifying the input to the user control. Moreover, since a user must be proactive in reacting and compensating for such conditions, a user must be mentally and physically capable of responding adequately to such conditions. Unfortunately, many individuals who use wheelchairs or other electrically operated vehicles do not have the sufficient physical abilities to react in an accurate and timely manner when a vehicle fails to operate in a desired manner. Accordingly, responsiveness of such a vehicle to an operator of the vehicle is unpredictable as well as unsafe.
In view of the above, it would be beneficial if a mechanism were created to compensate for motor or vehicle operating characteristics that vary over time or otherwise occur after initial production of the vehicle. Similarly, it would be desirable if a mechanism were capable of compensating for uneven burdens on the vehicle created by the operator of the vehicle. Moreover, it would be beneficial if such compensating mechanisms could be implemented through modifications made dynamically to a trim variable during operation of the vehicle.
Methods and apparatus for adjusting at least one of the motors in an electrically driven vehicle having a first motor for controlling a first wheel and a second motor for controlling a second wheel are disclosed. The method is performed in response to input from a user control that enables an operator of the vehicle to steer the vehicle. More particularly, it is determined from one or more conditions whether the operator of the vehicle is attempting to drive the vehicle straight on approximately level ground. When it is determined from the one or more conditions that the operator of the vehicle is attempting to drive the vehicle approximately straight on approximately level ground, it is then determined whether to adjust one of the motors based upon the input from the operator of the vehicle to the user control. When it is determined that adjustment is appropriate, the appropriate motor is adjusted.
Various conditions may be used to determine when the operator of the vehicle is attempting to drive the vehicle straight on approximately level ground. One condition is based upon the amount of adjustment of a user control by the operator of the vehicle, which may be determinative of the intention of the operator of the vehicle. In order to represent the positions of the user control, a traditional (x,y) coordinate system may be used where the user control is in a steady state at the origin of the coordinate system. Thus, the amount that the user control is adjusted along an x-axis may indicate a modification of a direction in which the vehicle is driven as well as an attempt to drive the vehicle straight (e.g., when the amount of adjustment is less than a threshold value). Similarly, an amount that the user control is adjusted along a y-axis may indicate a speed that the operator of the vehicle has selected. For example, when the operator of the vehicle extends the user control to its maximum length along the y-axis, this may indicate that the operator of the vehicle intends to proceed at maximum speed. Vehicle drivers typically proceed at maximum speed when they are driving approximately straight.
Another condition includes determining motor currents and motor speeds. The motor speeds and motor currents may be determinative of a variety of circumstances. For instance, different motor currents may indicate differing loads on the motors due to unlevel ground or uneven weight distribution within the vehicle.
Even when the operator of the vehicle is attempting to drive the vehicle straight on approximately level ground, motor adjustment may not be necessary. A determination whether adjustment is necessary is made based upon the input from the operator of the vehicle to the user control. For instance, positioning of the user control along the x-axis may indicate the amount of correction that may be required. This amount may then be compared with a threshold value (e.g., margin of error) to determine whether adjustment is appropriate or necessary.
Adjustment of the motors may be performed in a variety of ways. For instance, adjustment may include adjusting an input to one of the motors (e.g., voltage applied) to reduce the speed of the motor. The amount that a motor is adjusted may vary on a case-by-case basis or, alternatively, the amount that a motor is adjusted may be a predetermined amount that is applied in every case. Adjustment is preferably performed dynamically and automatically based upon the detection of one or more conditions and in response to input obtained from the operator of the vehicle. However, adjustment may also be initiated or performed manually by the operator of the vehicle in response to the notification of one or more conditions that indicate motor adjustment is desirable.